考虑孔洞影响的铸造镁合金ZM6疲劳寿命预估方法

铸造镁合金ZM6是一种应用于直升机减速器机匣制造的典型材料。然而，在铸造过程中产生的内部缺陷对材料的疲劳性能有显著影响。本文研究了含内部孔洞缺陷ZM6材料的疲劳损伤模型和寿命预估方法。首先，采用X射线断层扫描技术，对三个批次毛坯料制成的试验件进行扫描观察，获得了试验件内部孔洞的分布特征。进而，对48件试验件进行了两种应力比下多级应力水平的疲劳试验，获得了各批次试验件寿命结果，并通过观察与分析，得出了孔隙率和近表面较大孔洞为影响试验件疲劳寿命的两个关键因素。然后，基于损伤力学理论提出了通过材料初始弹性模量和等效孔洞局部应力应变场来分别反映孔隙率和近表面较大孔洞影响的疲劳损伤模型和寿命计算方法，并结合ABAQUS软件平台实现了含孔洞试验件的疲劳损伤计算和寿命计算。最后，采用所提理论模型和计算方法给出了试验件的疲劳寿命预测结果，并与试验结果进行了不同维度的对比，验证了所提模型与方法的有效性和适用性。

Study on fatigue life prediction method of cast magnesium alloy ZM6 considering the effect of internal pores

Cast magnesium alloy ZM6 is a typical material used in the manufacturing of helicopter reducer casing. However, the internal defects produced during the casting process have a significant effect on the fatigue properties of the material. In this paper, the fatigue damage model and life prediction method of ZM6 material with internal pore defects are studied. First, X-ray tomography scan of specimens made of three batches of blank material is conducted, and the distribution characteristics of internal pores is obtained. It can be observed that the pore distributions are much different for three batches of specimens. In addition, the randomly distributed small pores and few large dimension pores are both observed for each tested specimen, which will provide the basic data for the following influencing analysis of pores. Afterwards, high cycle fatigue tests of 48 specimens are conducted under two stress ratios and several stress levels, and the fatigue life results of each batch of specimens are obtained. After that, the correlation between life result and the distribution of internal pores is further studied. It can be concluded that the porosity and the large near-surface pores are the two key factors affecting the fatigue lives of specimens. Accordingly, based on the theory of damage mechanics, a fatigue damage model is then proposed to reflect the influences of porosity and large near-surface pores by introducing the initial elastic modulus of representative volume element (RVE) and the equivalent local stress and strain fields around the key pore. The corresponding parameters calibration method is presented as well. This model is then combined with the ABAQUS software platform to implement the numerical calculation of fatigue damage evolution of specimen with internal pores. Finally, the proposed theoretical model and calculation method are used to predict the fatigue lives of specimens, and the prediction results agree well with the experimental data, which validates the applicability of the proposed method.